Manufacture of methylolalkanes

ABSTRACT

A multistage tubular reaction system and method for preparing methylol derivatives of an aldehyde includes a tubular reaction system with a plurality of successive reactor stages provided with a formaldehyde containing feed stream. The system includes multiple feed ports for the staged addition of C 2  or higher condensible aldehyde and/or base to the formaldehyde containing stream at a plurality of successive feed points to provide a production stream, which is progressively provided with additional reactants as the production stream advances through the successive reaction stages. Advantages include better temperature control and reduced byproduct formation.

CLAIM FOR PRIORITY

This application is based International Application no.PCT/US2014/047738 FILED Jul. 23, 2014 entitled IMPROVED MANUFACTURE OFMETHYLOLALKANES which was based on U.S. Provisional Application No.61/862,574 filed Aug. 6, 2013, the priorities of which are herebyclaimed and the disclosures of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to improved manufacture of methylolalkanessuch as trimethylolpropane (TMP) by way of multistage reaction in atubular reactor with a plurality of tube banks. Staged addition ofreactant aldehyde and/or base promotes better temperature control andreduces unwanted byproducts such as 2-ethylhexyl dimers, methylolalkaneformals, methanol and so forth.

BACKGROUND

Manufacture of methylolalkanes is carried out in a variety of processesincluding by the reaction of formaldehyde with another aldehydecondensible with formaldehyde (hereinafter sometimes referred to asreactant aldehyde), that is, an aldehyde having at least one hydrogenbound at the α-carbon atom adjacent to the carbonyl moiety. Thebase-catalyzed aldol reaction of the reactant aldehyde with formaldehydeinitially generates the methylol derivative of the aldehyde in the firstreaction step. Then the aldehyde moiety may be converted in a secondreaction step by reaction with further formaldehyde and base in aCannizzaro-reaction into an alcohol group. Simultaneously, the formateof the base is generated. The 1^(st) reaction step, the aldol reaction,and the 2^(nd) reaction step, a Cannizzaro reaction, may either becarried out separately or in one working step. The bases used both forthe base catalyzed reaction step 1 and also for the reaction step 2which is stoichiometric in relation to the base quantity may optionallyeach independently be, for example, alkali metal or alkaline earth metalhydroxides, carbonates, or tertiary amines. In the so-called inorganicCannizzaro process, an inorganic base is used, such as sodium hydroxide,potassium hydroxide or calcium hydroxide. The resultant formates, suchas potassium formate or calcium formate can be used in furtherindustrial applications such as an assistant in the leather industry.

The reactions of formaldehyde with acetaldehyde, propionaldehyde,n-butyraldehyde and isobutyraldehyde are of particular interest. Thecorresponding reaction products are pentaerythritol, trimethylolethane,trimethylolpropane and neopentylglycol. These are polyhydric alcohols ofgreat industrial significance which find use, for example, in the fieldof coating resins, powder coating, foam production and polyesterproduction.

In particular, the manufacture of TMP according to the inorganicCannizzarro process is disclosed, for example, in U.S. Pat. Nos.3,183,274, 5,948,943, 7,253,326 and 8,354,561. Batchwise production ofTMP is seen in U.S. Pat. No. 7,253,326 to Eom et al., wherein the batchproduction is followed by a semi-continuous product recovery train.While batchwise production may be advantageous in terms of raw materialuse, such systems are relatively difficult to operate and capital costsare higher than continuous systems.

TMP is prepared from n-butyraldehyde and formaldehyde. In one preferredprocess, base-catalyzed aldol reaction initially generates2,2-dimethylolbutyraldehyde in a first reaction step which is thenconverted to a TMP-formate mixture by way of a Cannizzaro reaction. TheTMP-containing mixture is typically extracted with an organic solvent,such as ethyl acetate, thereby providing an organic phase comprising TMPand an aqueous phase containing the formate. The solvent is separatedand the crude TMP is purified by distillation. Typical processing isseen in U.S. Pat. No. 5,603,835 to Cheung et al., Comparative Example 1,Col. 7. See, also, U.S. Pat. No. 5,948,943 to Supplee et al. referred toabove.

The reaction of the aldehyde with formaldehyde is highly exothermic andcan result in excessively high temperatures in the reaction zone beforethe heat can be removed. The temperature spikes lead to efficiencylosses due to side reactions. In order to reduce said temperaturespikes, the art generally teaches to use a relatively dilute aqueousformaldehyde solution and aqueous solution of the inorganic base inorder to moderate temperature. Because of the presence of large amountsof water in the reaction mixture, the heat capacity is relatively highso that the exothermic heat of the reaction does not raise thetemperature of the mixture to a level above the desired range.

Besides the large amount of water, it is conventionally typical to useformaldehyde in substantial excess over the theoretical amount based onthe reactant aldehyde. In cases where n-butyraldehyde is reacted withformaldehyde to produce trimethylolpropane the art teaches generally aformaldehyde excess of about 1 to 7 moles or so over the formaldehydeneeded for the actual reaction.

Commonly, the aqueous formaldehyde solution is blended with the startingaldehyde continuously to produce a stream of aqueous mixed aldehydes andthe aqueous solution of the inorganic base is injected into this streamin a mixing zone. The reaction mixture is then fed to a reaction zone.Heat generation is most problematical at or near the mixing zone wherethe reactants are most highly concentrated. Heat generated in theseareas leads to temperature spikes and byproduct generation. As will beappreciated from the foregoing references, byproducts can cause colorand other product quality problems, leading to higher purificationexpense in addition to loss of efficiency because of lower yields.Moreover, large amounts of water needed as a temperature moderator aredifficult and expensive to process.

SUMMARY OF INVENTION

In connection with methylolalkane manufacture, byproducts can be reducedsignificantly if the reaction of the aqueous formaldehyde, a C₂ orhigher condensible aldehyde and the aqueous solution of the inorganicbase are conducted in a tube reactor where the reactants are added instages at various tubes up to the required amount. So also, heatgeneration is less localized and better temperature regulation isachieved. Optionally, tube inserts are used to promote heat transfer andmixing, preferably proximate a plurality of feed ports. Variousconfigurations and types of tube inserts are commercially available fromKoch Heat Transfer Company and their use is discussed in ChemicalEngineering Process, September 2012, pages 19-25; Shilling, Richard, L.;the disclosure of which is incorporated herein by reference.

The tube reactor according to another aspect of the invention comprisesa series n of tubes and each series contains m single tubes, where m canvary between reactor stages. The staged addition of the reactants inaccordance with the invention occurs at various locations and preferablyin the first tube of a series of tubes. In particular the aldehyde andthe aqueous solution of the inorganic base are added to the variousstages while the aqueous formaldehyde solution flows through the tubereactor.

The tube reactor is designed as a double-pipe reactor with the reactionzone in the inner tube and a coolant in the outer tube, sometimesreferred to herein as a jacketed construction as discussed hereinafter.

Further details and advantages will become apparent from the discussionwhich follows.

DESCRIPTION OF DRAWINGS

The invention is described in detail below in connection with numerousexamples and in connection with the attached FIGS. In the FIGS:

FIG. 1 is a schematic diagram illustrating the inventive processemploying a tube reactor with the staged addition of n-butyraldehyde andan aqueous solution of potassium hydroxide wherein each series of tubeshas a temperature indication controller which is used to control a valvemanipulating the cooling flow through that series depending on the heatof reaction generated in that series;

FIG. 2 is a schematic sectional view of a reactor tube with a tubeinsert residing in a cooling conduit;

FIG. 3 is a view in perspective of a section of reactor tube providedwith a wire-wrapped displacement insert;

FIG. 4 is a view in perspective of a static mixer tube insert; and

FIGS. 5(a) to 5(d) are views in perspective of 4 different types ofswirl tube inserts.

DETAILED DESCRIPTION

The invention is described in detail below in connection with the FIGS.for purposes of illustration, only. The invention is defined in theappended claims. Terminology used throughout the specification andclaims herein is given its ordinary meaning as supplemented by thediscussion immediately below.

“Aggregate” and like terminology refers to the total amount of reactantsor material added to the reaction system by adding the amounts suppliedto each stage. For example, the aggregate amount of reactant aldehydeadded to the system includes the sum of the amounts supplied at eachstage.

A C₂ or higher condensible aldehyde is a two carbon or more carbonaldehyde which will undergo condensation with formaldehyde to form amethylol derivative of that aldehyde. Aldehydes condensible withformaldehyde have at least one hydrogen bound at the α-carbon atomadjacent to the carbonyl moiety. Useful higher aldehydes are virtuallyall alkanals having an acidic hydrogen atom in the α-position to thecarbonyl group. Aliphatic aldehydes having from 2 to 24 carbon atoms maybe used as starting materials and may be straight-chain or branched orelse contain alicyclic groups. Equally, araliphatic aldehydes aresuitable as starting materials, provided that they contain at least onehydrogen in the α-position to the carbonyl group. In general, aralkylaldehydes having from 8 to 24 carbon atoms, preferably from 8 to 12carbon atoms, are used as starting materials, for example phenylacetaldehyde. Preference is given to aliphatic aldehydes having from 2to 12 carbon atoms. Especially preferred C₂ or higher condensiblealdehydes include acetaldehyde, propionaldehyde, n-butyraldehyde andisobutyraldehyde.

Unwanted byproducts avoided in accordance with the invention includedimers such as 2-ethylhexyl dimers produced by self-aldol condensationof butyraldehyde and may include a plurality of impurities believedderived from reaction of monomethylol compounds such as monomethylolbutyraldehyde. Such impurities include for, example,

-   -   monocyclic TMP-formal (MCF):

-   -   monolinear bis-TMP-formal (MBLF or TMP-BMLF):        [C₂H₅C(CH₂OH)₂CH₂O]₂CH₂        -   Methyl-(monolinear)TMP-formal:            C₂H₅C(CH₂OH)₂CH₂OCH₂OCH₃

and di-TMP:

-   -   2[2,2-bis(hydroxymethyl)butoxymethyl]-2-ethylpropane-1,3-diol

In a process including a Cannizzarro process, staging base addition alsoreduces unwanted methanol generation which increases raw materialefficiency.

As used herein, a Cannizzarro process refers to methyloalkane synthesiswhere the condensate intermediate is reacted with additionalformaldehyde and base to yield the corresponding methylolalkane, forexample, a Cannizzarro TMP synthesis as shown in the following scheme:

“Tube insert” and like terminology refers to a part disposed in areaction tube to enhance mixing and heat transfer. A tube insert may bea static mixer insert, a boundary layer interrupter insert, a swirl flowinsert, a displaced flow insert or a combination of these types ofinserts. Particularly preferred is a wire-wrapped displacement flowinsert which combines swirl flow and displacement flow augmentation.Displaced-flow inserts increase heat transfer by blocking flow furthestfrom the tube wall and increasing the Reynolds number of the liquid andtherefore the U-value of the system. In connection with the presentinvention, it also extends the area in which the reaction is occurring,which, in turn, reduces the final peak temperature seen in the reactorby increasing the amount of area used for heat transfer in criticalareas. By using a wire-wrapped tube insert, some swirl flow is inducedas well, which imparts a helical flow path which further increases themixing and turbulence at the wall, which may be operable to change flowfrom a laminar operation to a turbulent operation in that tube,depending upon conditions. In preferred embodiments employing displacedflow inserts, the ratio of D/D_(e) (defined below) is from 1.5 to 3. Inthe most preferred embodiments, inserts are used in selected sections ofreactor pipe only so as not to overtax the feed pumps of the reactionsystem.

“Heat transfer equivalent diameter” or D_(e) is defined by therelationship:

${De} = \frac{4\;{Nfa}}{\pi\; D}$where Nfa is the net free area inside of the tube and D is the (inside)diameter of the tube.

“Methylol derivative” and like terminology refers to condensationproducts of formaldehyde and aldehydes condensible with formaldehyde aswell as the corresponding polyol end products formed by reduction of thecondensation product with formaldehyde or hydrogenation. Methylolderivatives include methylolalkanes and methylolaldehydes.

“Proximate” refers to closeness in position of a feed port and generallymeans that a feed point is proximate to a reactor tube section with atube insert if less than 30% of added reactant aldehyde reacts over areactor length prior to entry into the reactor tube section with a tubeinsert or if the feed point is at a distance of less than 6 meters fromthe reactor tube section with a tube insert. In preferred embodiments, aproximate feed point is within a distance of 6 meters of a reactor tubesection with a tube insert and still more preferably a proximate feedpoint is within a distance of 5 meters of a reactor tube section with atube insert. In many cases a proximate feed point is within a distanceof 3 meters of a reactor tube section with a tube insert.

A “stage” of a multistage reaction system is a portion of the reactorsystem discretely configured with respect to other stages by way of anadditional feed port for reactants or catalyst or independenttemperature control of the stage, or by way of a separate flow ofcooling medium to the stage.

“Successive” refers to a serial arrangement of reactor stages, forexample, where later reaction stages are downstream of initial stages asis seen in FIG. 1.

Referring to FIG. 1, there is illustrated schematically a reactionsystem 10 comprising multiple banks or stages S1, S2, S3 and so forth ofreaction tubes such as tubes indicated at 12, 14, 16 and so forth. Eachbank preferably has multiple tubes connected in series within each bankas shown schematically. 3,4,5,6 or more stages may be employed, eachhaving 3-10 tubes in series if so desired. Stages without additionalreactant feed may be interposed between stages receiving fresh chargesof reactants.

Reaction system 10 also includes a cooling system which includes aplurality of coolant feeds 20 for providing coolant to the reactiontubes and a plurality of return lines 22 for returning coolant to thecooling system. Also provided are a plurality of temperature indicatorcontrollers 24, 26, 28, 30, a cooler 35, and a plurality of controlvalves indicated at 40, 42, 44, and 46.

The reaction tubes are connected in series as indicated schematicallyand have the structure generally illustrated in FIGS. 2 and 3, althoughonly the tubes receiving a fresh charge of aldehyde reactant need beprovided with a tube insert to enhance mixing and heat transfer.Likewise, reactor stages without additional reactant feed may includeinlet tubes without tube inserts since the stream concentration profilesare already relatively well developed.

Referring to FIGS. 2 and 3, there is shown reaction tube 12, which hasan outer shell 60, and annular cooling channel 62 and an inner reactiontube 64 which is provided with a tube insert 66. The reaction tube hasan inside diameter, D. Preferably, insert 66 is a wire-wrapped cylinder,a combination swirl flow and displacement insert which reduces residencetime in the areas where reactants are introduced and heat transfer ismost critical.

Insert 66 thus has a cylindrical body 68, a wire wrap 70 and resides inreaction tube 64 as shown in FIG. 3. The net free area 72 is thusdefined between insert 66 and the inner wall of tube 64.

The reaction tubes in system 10 without inserts are of the same generalconfiguration, but the inner channel is unrestricted.

In preferred cases, the reaction tubes with inserts have a ratio of D/Deof from 1.5 to 3 as noted above.

Instead of a wire wrapped displacement insert, a static mixer inserthaving the geometry shown in FIG. 4 could be utilized. Static mixers areoperative to transport, by their mechanical construction, the fluid atthe tube wall to the center of the tube and to fold these transportedregions of fluid into each other. This dramatically increases heattransfer because it increases the local temperature difference betweenportions of the bulk (tubeside) fluid and the tube wall. Static mixersare particularly useful in a flow that is laminarized.

Alternatively, a swirl flow tube insert such as the twisted tape swirlinserts shown in FIGS. 5(a)-5(d) could be employed, if so desired.Twisted tapes impart rotational flow which has two effects. It imparts ahelical flow path along the inside wall of the tube, thereby producing ahigh velocity along the tube wall that is a function of the helical flowangle. It also imparts a combination of flow rotation and centripetalforce away from the center of the tube that in single-phase flow,increases mixing and turbulence at the tube wall. This creates turbulentflows at Reynolds numbers that would be characteristic of laminar ortransition flows in tubes without inserts. Inducing turbulence at alower Reynolds number enhances heat transfer.

In operation, a stream 100 of aqueous formaldehyde is fed to system 10via reaction tube 12 of bank S1 along with potassium hydroxide andn-butyraldehyde via a feed port 101. Tube 12 has a tube insert asdiscussed in connection with FIGS. 2 and 3. After passing through tube12, the reaction mixture proceeds through additional tubes in bank S1where the reaction proceeds and stream 100 becomes enriched inmethylolated product before being passed to the next stage of thesystem.

Additional potassium hydroxide and n-butyraldehyde is provided to stream100 via another feed port 102 as the stream is fed to reactor stage S2wherein the first tube is provided with a tube insert as discussedabove. Stream 100 proceeds through the tubes of stage S2 such as tube 14before exiting the stage.

The outlet of bank S2 is optionally provided with cooler 35 to furtherregulate temperature in the system.

After exiting bank S2 and cooler 35, stream 100 is provided withadditional butyraldehyde and potassium hydroxide at a feed portindicated at 103 and fed to reactor tube bank S3 as shown. The firsttube of bank S3 is likewise provided with a tube insert, whereas thesubsequent tubes of the bank need not have inserts.

Stream 100 is passed through the tubes of bank S3 and thereafter stilladditional butyraldehyde and potassium hydroxide may be added insubsequent stages if so desired, or the stream may be provided toadditional reactor banks without further providing reactants.

During operation of system 10 as described above, the temperature in thereaction tubes is regulated independently in the various reaction tubebanks by way of a plurality of temperature indicator controllers(TIC's), control valves and one or more coolers such as cooler 35.Generally, the temperature in the reaction medium is maintained between35° C. and 75° C. Preferably, the temperature in the reaction medium ismaintained at between 35° C. and 65° C. at all times and temperaturespikes are minimized or eliminated.

To this end, coolant feed 20 is pumped to reactor banks S1, S2 and S3such that the coolant circulates through the annular cooling channels ofthe reaction tubes before returning to the coolant system via returnlines 22. TIC controllers sense the temperature of the coolant andregulate control valves in order to maintain a target temperature of thecoolant thus maintaining a target temperature of the reaction medium aswell. The controllers and valves are configured such that thetemperature of each stage can be independently controlled.

TIC's 24, 26, 30 sense the reaction temperature in banks S1, S2 and S3and regulate the flow of the coolant through valves 40, 42, 46 in orderto maintain target reaction temperatures in the banks. Another TIC 28senses temperature in cooler 35 and controls coolant flow via valve 44to further adjust temperatures in the system.

The inventive system may be sized and operated in a variety of operatingmodes wherein reactants and catalyst are added in stages to minimizetemperature spikes and maintain target temperatures.

The amount of reactants employed will vary depending upon the processemployed and the products made; for example, the aggregate formaldehyde:C₂ and higher aldehyde reactant mole ratio differs with the C₂ andhigher aldehyde reactant. If a Cannizzaro reaction scheme is included,acetaldehyde requires a minimum of ratio of formaldehyde:acetaldehyde of4:1, n-butyraldehyde requires a minimum of ratio offormaldehyde:n-butyraldehyde of 3:1, and isobutyraldehyde requires aminimum of ratio of formaldehyde:isobutyraldehyde of 2:1. Forn-butyraldehyde recommended ranges of formaldehyde: butyraldehyde arefrom 3.01:1 to 10:1.

A set of preferred operating parameters for making TMP fromn-butyraldehyde in a Cannizzarro process are as follows:

Reaction Medium 35° C.-65° C. Temperature Aqueous Formaldehyde 10%-50%Concentration (wt % Formaldehyde) Aggregate Formaldehyde/Reactant3.01:1-10:1 Aldehyde Molar Ratio Aggregate Inorganic Base/Reactant1:1-2:1 Aldehyde Molar Ratio preferably 1:1-1.5:1

Introducing the aldehyde in increments raises the effectiveformaldehyde/reactant aldehyde ratio and reduces the formation of dimersthrough self-condensation of the C₂ or higher condensable aldehyde. Soalso, staged addition of base lowers the base/formaldehyde ratio in theinitial stages and reduces methanol generation in connection with aCannizzarro process. Various operating schemes include the schemes (a),(b) and (c):

-   -   (a) Wherein the C₂ or higher condensible aldehyde is added in a        fixed proportion with inorganic base at said plurality of        successive feed points to provide a production stream which is        progressively provided with additional C₂ or higher condensible        aldehyde as the production stream advances through the        successive reaction stages;    -   (b) Wherein the C₂ or higher condensible aldehyde and inorganic        base are provided in an upstream feed point in larger amounts        relative to amounts provided in a downstream feed point.        Providing larger portions of reactants in early stages provides        additional residence time and is desirable if adequate cooling        is available in the system. One preferred protocol in a        Cannizzarro process is to provide 30-60% of the aggregate amount        of both the base and the C₂ or higher condensible aldehyde in        early reaction stage(s);    -   (c) Wherein the inorganic base is provided in a downstream feed        point in a larger amount relative to an amount provided in an        upstream feed point to provide a production stream which is        provided with inorganic base at higher levels in a later stage        as compared with levels of inorganic base in an initial stage.

Said process options may include the option of using different ratios ofbase and condensable aldehyde along the feeding points, as long as thetotal of all additions equals the targeted component ratios.

After the production stream 100 exits the last bank of the reactionsystem, further work-up includes extracting formates from the reclaimedTMP and distillation of the crude TMP to purified form as is known inthe art. Typically, purification of the crude product includes amultistage water/ethyl acetate extraction system, as well as one or moredistillation tower (s).

The process and apparatus of the present invention are especially suitedto the inorganic Cannizzarro process of the class described in U.S. Pat.Nos. 3,183,274, 5,948,943, 7,253,326 and 8,354,561 referred to above.Alternatively, the apparatus and process methodology could be employedin connection with an organic Cannizzarro process or acondensation/hydrogenation methylolalkane process described in U.S. Pat.No. 7,301,058.

There is thus provided in accordance with the present invention a methodof making a methylolalkane from formaldehyde and a C₂ or highercondensable aldehyde in a multistage process comprising: (a) providing aformaldehyde containing stream to a tubular reaction system with aplurality of successive reaction stages; (b) adding a C₂ or highercondensible aldehyde and optionally a base to the formaldehydecontaining stream wherein at least one of the C₂ or higher condensiblealdehyde or base are added to the formaldehyde containing stream at aplurality of successive feed points to provide a production stream whichis progressively provided with additional C₂ or higher condensiblealdehyde or base as the production stream advances through thesuccessive reaction stages; and (c) converting the C₂ or highercondensible aldehyde and formaldehyde to a methylolalkane.

The C₂ or higher condensible aldehyde may be added to the formaldehydecontaining stream at a plurality of successive feed points to provide aproduction stream which is progressively provided with additional C₂ orhigher condensible aldehyde as the production stream advances throughthe successive reaction stages.

In various methods of the invention, the methylolalkane may bepentaerythritol and the C₂ or higher condensible aldehyde isacetaldehyde or the methylolalkane is trimethylolethane and the C₂ orhigher condensible aldehyde is propionaldehyde. Likewise, themethylolalkane may be trimethylolpropane and the C₂ or highercondensible aldehyde is n-butyraldehyde or the methylolalkane may beneopentyl glycol and the C₂ or higher condensible aldehyde isisobutyraldehyde.

The base may be added to the formaldehyde containing stream at aplurality of successive feed points to provide a production stream whichis progressively provided with additional base as the production streamadvances through the successive reaction stages if so desired or boththe C₂ or higher condensible aldehyde and an inorganic base may be addedto the formaldehyde containing stream at a plurality of successive feedpoints to provide a production stream which is progressively providedwith additional C₂ or higher condensible aldehyde and inorganic base asthe production stream advances through the successive reaction stages.

Throughout the various aspects of the invention, an inorganic baseselected from potassium hydroxide, calcium hydroxide and sodiumhydroxide may be employed.

Preferably, the inorganic base and C₂ or higher condensible aldehyde isadded to the production stream in at least 3 discrete locations and insome cases in at least 4 discrete locations.

While different numbers of stages may be employed, preferably thetubular reaction system has at least 3 stages.

Typically, the temperature of the production stream is maintainedbetween 30° C. and 75° C.; more preferably in many cases the temperatureof the production stream is maintained between 35° C. and 65° C.

In some embodiments, said C₂ or higher condensible aldehyde is added ina fixed proportion with inorganic base at said plurality of successivefeed points to provide a production stream which is progressivelyprovided with additional C₂ or higher condensible aldehyde as theproduction stream advances through the successive reaction stages. Instill other embodiments, said C₂ or higher condensible aldehyde andinorganic base are provided in an upstream feed point in larger amountsrelative to amounts provided in a downstream feed point.

In still other cases, the inorganic base is provided in a downstreamfeed point in a larger amount relative to an amount provided in anupstream feed point to provide a production stream which is providedwith inorganic base at higher levels in a later stage as compared withlevels of inorganic base in an initial stage.

In another aspect of the invention, there is provided a multistagetubular reaction system for preparing methylol derivatives of a C₂ orhigher condensible aldehyde comprising: (a) a tubular reaction systemwith a plurality of successive reactor stages comprising a plurality ofreaction tubes; (b) a reaction system inlet adapted to provide aformaldehyde containing stream to the tubular reaction system; and (c) aplurality of feed ports adapted to provide at least one of the C₂ orhigher condensible aldehyde or a base to the formaldehyde containingstream at a plurality of successive feed points to provide a productionstream which is progressively provided with additional C₂ or highercondensible aldehyde or base as the production stream advances throughsuccessive reaction stages. The multistage tubular reaction system ispreferably adapted to provide both C₂ or higher condensible aldehyde andbase to the successive stages of the reaction system such that theproduction stream is progressively provided with additional C₂ or highercondensible aldehyde and base as the production stream advances throughsuccessive reaction stages.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. Such modifications are also to be considered aspart of the present invention. In view of the foregoing discussion,relevant knowledge in the art and references discussed above inconnection with the Background of the Invention, the Summary ofInvention and Detailed Description, the disclosures of which are allincorporated herein by reference, further description is deemedunnecessary. In addition, it should be understood that aspects of theinvention and portions of various embodiments may be combined orinterchanged either in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention.

What is claimed is:
 1. A method of making a methylolalkane fromformaldehyde and a C₂ or higher condensable aldehyde in a multistageprocess comprising: (a) providing a formaldehyde containing stream to atubular reaction system with a plurality of successive reaction stages;(b) adding a C₂ or higher condensible aldehyde and optionally a base tothe formaldehyde containing stream wherein at least one of the C₂ orhigher condensible aldehyde or base are added to the formaldehydecontaining stream at a plurality of successive feed points to provide aproduction stream which is progressively provided with additional C₂ orhigher condensible aldehyde or base as the production stream advancesthrough the successive reaction stages; and (c) converting the C₂ orhigher condensible aldehyde and formaldehyde to a methylolalkane.
 2. Themethod according to claim 1, wherein the C₂ or higher condensiblealdehyde is added to the formaldehyde containing stream at a pluralityof successive feed points to provide a production stream which isprogressively provided with additional C₂ or higher condensible aldehydeas the production stream advances through the successive reactionstages.
 3. The method according to claim 1, wherein the methylolalkaneis trimethylolpropane and the C₂ or higher condensible aldehyde isn-butyraldehyde.
 4. The method according to claim 1, wherein themethylolalkane is neopentyl glycol and the C₂ or higher condensiblealdehyde is isobutyraldehyde.
 5. The method according to claim 1,wherein base is added to the formaldehyde containing stream at aplurality of successive feed points to provide a production stream whichis progressively provided with additional base as the production streamadvances through the successive reaction stages.
 6. The method accordingto claim 5, wherein said base is an inorganic base selected frompotassium hydroxide, calcium hydroxide and sodium hydroxide.
 7. Themethod according to claim 1, wherein said tubular reaction system has atleast 3 stages.
 8. The method according to claim 1, comprising addingthe C₂ or higher condensible aldehyde and an inorganic base to theformaldehyde containing stream at a plurality of successive feed pointsto provide a production stream which is progressively provided withadditional C₂ or higher condensible aldehyde and inorganic base as theproduction stream advances through the successive reaction stages. 9.The method according to claims 8, wherein said inorganic base isselected from potassium hydroxide, calcium hydroxide and sodiumhydroxide.
 10. The method according to claim 8, wherein said C₂ orhigher condensible aldehyde is added in a fixed proportion withinorganic base at said plurality of successive feed points to provide aproduction stream which is progressively provided with additional C₂ orhigher condensible aldehyde as the production stream advances throughthe successive reaction stages.
 11. The method according to claim 10,wherein said C₂ or higher condensible aldehyde and inorganic base areprovided in an upstream feed point in larger amounts relative to amountsprovided in a downstream feed point.
 12. The method according to claim8, wherein said inorganic base is provided in a downstream feed point ina larger amount relative to an amount provided in an upstream feed pointto provide a production stream which is provided with inorganic base athigher levels in a later stage as compared with levels of inorganic basein an stage.
 13. The method according to claim 1, wherein thetemperature of the production stream is maintained between 30° C. and75° C.
 14. A multistage tubular reaction system for preparing methylolderivatives of a C₂ or higher condensible aldehyde comprising: (a) atubular reaction system with a plurality of successive reactor stagescomprising a plurality of reaction tubes cooled with a coolant in orderto maintain a desired temperature; (b) a reaction system inlet adaptedto provide a formaldehyde containing stream to the tubular reactionsystem; and (c) a plurality of feed ports adapted to provide at leastone of the C₂ or higher condensible aldehyde or a base to theformaldehyde containing stream at a plurality of successive feed pointsto provide a production stream which is progressively provided withadditional C₂ or higher condensible aldehyde or base as the productionstream advances through successive reaction stages, wherein thetemperature of the production stream is maintained between 30° C. and75° C.
 15. The multistage tubular reaction system for preparing methylolderivatives of a C₂ or higher condensible aldehyde according to claim14, wherein the reaction system comprises a plurality of reaction tubesof a jacketed construction with an outer shell, an annular coolingchannel and an inner reaction tube defining a reaction zone and whereinthe annular cooling channel receives coolant.
 16. A multistage tubularreaction system for preparing methylol derivatives of a C₂ or highercondensible aldehyde comprising: (a) a tubular reaction system with aplurality of successive reactor stages comprising a plurality ofreaction tubes cooled with a coolant in order to maintain a desiredtemperature; (b) a reaction system inlet adapted to provide aformaldehyde containing stream to the tubular reaction system; and (c) aplurality of feed ports adapted to provide at least one of the C₂ orhigher condensible aldehyde or a base to the formaldehyde containingstream at a plurality of successive feed points to provide a productionstream which is progressively provided with additional C₂ or highercondensible aldehyde or base as the production stream advances throughsuccessive reaction stages, wherein the reaction system comprises aplurality of reaction tubes of a jacketed construction with an outershell, an annular cooling channel and an inner reaction tube defining areaction zone and wherein the annular cooling channel receives coolant.